The invention relates to a formulation for an antifouling coating system for application to submerged substrates, a method for treatment with such a formulation of substrates to be submerged, and the use of such a formulation as an antifouling agent for inhibiting the attachment of marine organisms such as algae, shellfish and other crustaceans in any submerged substrate, and in particular ship hulls.
A submerged substrate is spontaneously colonized by marine organisms. This is a quite normal phenomenon under water, especially in the light-receiving and nutrient-rich layers.
Indeed, the sea which, in a broad sense, is a vast expanse of salt water and, to a lesser extent, freshwater, is naturally rich in proteins and polysaccharides, produced mainly by plankton and the excreta of the multitude of aquatic organisms that can be found in seawater. The surface of the sea or freshwater, when it is not very rough, is thus permanently covered with a biofilm. Below the water's surface, the suspended elements are deposited onto any submerged substrate in the form of a film having a thickness of a few microns, after only a few seconds or minutes in a rich medium. This film provides some types of bacteria, microalgae and aquatic microscopic fungi, known as pioneer organisms, with an initial source of nutrients. These then enrich the film, which thickens into a thicker mucilaginous biofilm, thus becoming a substrate for increasingly complex colonies of protozoa, and then for fixed or mobile organisms (macro-algae, larvae of invertebrates and vertebrates), including encrusting species, which themselves become a substrate for other species. In addition, many marine organism larvae have amazing fixation capabilities, even on living, flexible and highly mobile substrates, as is the case with barnacles on the skin of whales.
Thus, it is known that the final layer of paint or coating, applied for example to the hull of a ship before its launch, should preferably be of the antifouling type. Indeed, this helps protect the submerged part of the hull against the attachment of such marine organisms.
However, most anti-fouling paints and other coatings available on the market, in particular before the introduction of the new environmental standards in force to date, are primarily made from biocides, starting products that are extremely harmful to the environment and humans. They are harmful, on the one hand to the marine or river environment, due to poisoning of fauna and flora, and on the other hand to the person who applies or cleans them.
Thus, these paints could contribute to certain phenomena of dystrophization and overgrowth of undesirable species. The species of phytoplankton and zooplankton that are most sensitive to biocides are disappearing, in favor of unwanted or toxic algae. Some biocides and other pollutants can also accumulate in the biofilm which forms on the surface of calm waters and be “exported” with sprayed water to the coast and inland areas during storms, to such an extent as to affect or even kill the most fragile plants of the coastal strip.
In addition, the immediate risks for the person who handles them are irritating for the lungs, allergic and cutaneous. This is referred to as direct toxicity to humans. Without adequate protection, any user may indeed inhale these particles, for example when using a spray gun, or when sanding the antifouling layer from a hull, or they may pass through the skin after contact with projections or paint, or more rarely via accidental ingestion, or more rarely even by voluntarily ingesting paint chips (for example, with the phenomenon known as “pica”). Such anti-fouling paints can also induce indirect toxicity in humans, through the ingestion of filtering shellfish, such as mussels, oysters, clams, etc. or other seafood or fish that have grown downstream from dry docks (painting or stripping of ship hulls) or close to submerged wrecks. Regular consumption of contaminated seafood is likely to induce acute or chronic diseases associated with heavy metals. Concerning the long-term risks, these are still poorly understood, but could include degenerative diseases, autoimmune diseases, or cancer.
The application of biocide-based antifouling paints must therefore always be carried out using protection for the skin and mucous membranes (dry suits, goggles, gloves) and respiratory protection (cartridge respirator).
In addition, decomposition by burning of most biocide-based antifouling paints, which have a flash point of less than 55° C. and are thus considered flammable, also leads to the release of highly toxic gases, fumes and ashes.
Such biocide-based anti-fouling paints thus contain one or more toxic molecules and are proven to be polluting.
In particular, these include tributyltin (TBT), which is very effective and has been the most widely used biocide in the maritime field throughout the world. However, this product and its degradation molecules and metabolites have turned out to be serious and lasting pollutants, to the point of decimating natural populations of shellfish and disrupting the breeding of many species. In particular, in some organisms TBT induces an imposex phenomenon at very low dilutions, below one ng/L. TBT residues, including tin, which is non-biodegradable, are long-lasting in harbor sediments and at dredged mud dumping sites, and downstream of these, as a consequence of their potential re-suspension. For these reasons, in November 1999, a resolution of the IMA (A.895) was proposed and adopted on Oct. 5, 2001, prohibiting tin-based antifouling paints as of 1 Jan. 2003. Their presence on ships' hulls has been prohibited since 2008.
Also known are other anti-fouling paints from the family of biocides, which prove less toxic, but nevertheless remain so. According to the European Commission project “Assessment of Antifouling Agents in Coastal Environment,” the analysis of residues released into the water by these paints reveals the presence of copper, in particular in the form of cuprous oxide, copper dioxide, copper thiocyanate, copper acrylate, copper powder in the form of flakes, copper hydroxide, zinc in the form of zinc pyrithione, copper-nickel, or also rosin (or rosine). Also, among the biocides released into the water, those mostly found were organochlorines such as dichlorophenyl dimethyl urea (diuron), 2-methylthio-4-tert-butylamino-6-cyclopropylamino-s-triazine (Irgarol 105®I) 2,4,5,6-tetrachloroisophthalonitrile (chlorothalonil), 4,5 dichloro-2-n-octyl-4-isothiazolin-3-one (Seanine 211® Kathon 5287®), and dichlorofluoro methylthiodimethyl phenyl sulfamide (dichlofluanid). Also found, although less often and in smaller quantities, were 2-thiocyanomethylthio benzothiazole (TCMTB), 2,3,5,6-tetrachloro-4-sulfuronyl pyridine (TCMS pyridine), zinc dithio carbamate (zineb), arsenic trioxide. These biocides sometimes become associated with one another and/or copper, achieving synergistic effects, and strengthening or broadening their spectrum of action.
In general, there is a genuine need for products or preparations that are free of any toxic biocide, that are much less harmful to human and animal health, and just as effective. In the present context, particularly. In the context of biocide regulation, it would be desirable to find an antifouling paint or coating, which would be less irritating and less toxic, at least as effective as paints containing biocides, without having the adverse effects of the prior art paints.
Biocide-free antifouling coatings with anti-adhesion properties against the attachment of marine organisms have been tested and developed, based for example on liquid organosilicones, or liquid paraffin or fluorinated oils in combination with polymers of the organopolysilicone type. The mode of action of these coatings is based on the lower surface tension of silicone and on the more or less controlled release of lubrication additives used to prevent the attachment of marine organisms. However, the effectiveness of these antifouling coatings is limited. Another disadvantage is their low mechanical load capacity, which is frequently associated with insufficient adhesion to anti-corrosive coatings, thus requiring the application of an intermediate tie layer.
More particularly, from U.S. Pat. No. 6,413,446 an antifouling agent is known, which comprises in particular carbosiloxanes, alkoxysilanes, an organic solvent and/or water, a catalyst, inorganic nanoparticles as well as lubricant additives. However, this agent appears to comprise only a very small amount of anti-adhesion lubricating agent in addition to silicone resins.
From EP 0 563 939 a formulation is known, which contains a silicone resin, a silicone fluid and a solvent to form an antifouling coating in which the silicone fluid forms a liquid interface on top of the resin layer and prevents the flora and fauna from attaching firmly to the substrate surface. Such an antifouling coating undergoes a phase shift and is not homogeneous.
Also known from EP 1 829 943 is an antifouling coating composed of a composition comprising an organopolysiloxane and paraffin or silicone oil. Paraffin or silicone oil exude at the surface of the film formed by the coating and contribute to the antifouling performance. Such an antifouling coating also undergoes a phase shift and is not homogeneous.
Finally, from JP 08 081 524 an antifouling composition is known, which comprises a silicone resin emulsion and optionally a wax or an oil-based emulsion. However, such compositions do not prove to be stable over time.